y to the red one, which was attracted least, and the last of
them all. I afterwards cut out nine square pieces of gauze of the same
colors with the ribbons, and having put them one after another on a hoop
of wood, with leaf-gold under them, the leaf-gold was attracted through
all the colored pieces of gauze, but not through the white or black.
This inclined me first to think that colors contribute much to
electricity, but three experiments convinced me to the contrary. The
first, that by warming the pieces of gauze neither the black nor white
pieces obstructed the action of the electrical tube more than those of
the other colors. In like manner, the ribbons being warmed, the black
and white are not more strongly attracted than the rest. The second
is, the gauzes and ribbons being wetted, the ribbons are all attracted
equally, and all the pieces of gauze equally intercept the action of
electric bodies. The third is, that the colors of a prism being thrown
on a white gauze, there appear no differences of attraction. Whence it
proceeds that this difference proceeds, not from the color, as a color,
but from the substances that are employed in the dyeing. For when I
colored ribbons by rubbing them with charcoal, carmine, and such other
substances, the differences no longer proved the same."

In connection with his experiments with his thread suspended on glass
poles, Dufay noted that a certain amount of the current is lost, being
given off to the surrounding air. He recommended, therefore, that the
cords experimented with be wrapped with some non-conductor--that it
should be "insulated" ("isolee"), as he said, first making use of this
term.

DUFAY DISCOVERS VITREOUS AND RESINOUS ELECTRICITY

It has been shown in an earlier chapter how Von Guericke discovered
that light substances like feathers, after being attracted to the
sulphur-ball electric-machine, were repelled by it until they touched
some object. Von Guericke noted this, but failed to explain it
satisfactorily. Dufay, repeating Von Guericke's experiments, found
that if, while the excited tube or sulphur ball is driving the repelled
feather before it, the ball be touched or rubbed anew, the feather comes
to it again, and is repelled alternately, as, the hand touches the ball,
or is withdrawn. From this he concluded that electrified bodies first
attract bodies not electrified, "charge" them with electricity, and then
repel them, the body so charged not being attrac